How Does the Age of a Seed Affect Its Ability to Germinate?

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That packet of pole bean (Phaseolus vulgaris) seeds sat over the winter one year because of a bumper crop and the second year, it was covered by new packets of seeds. When you find it the third year, the question is whether any of those seeds will germinate and produce strong young plants. Odds are, those beans will grow, but there are more prudent ways to tell than just gambling.

Seeds and Age

All living things age, including seeds, which contain embryonic plants, lying dormant, waiting to break their protective coats and push through the soil. As a seed ages, the tiny living plant consumes the nutrients stored inside the seed around it. When all the nutrients are consumed, the embryo must grow or wither. Some seeds lose viability rather quickly, but others contain plants that have well-developed survival mechanisms. In a field in California, for example, seeds of branched broomrape (Orobanche ramosa), a virulently parasitic weed, reappeared after two decades. The plants grew despite repeated glyphosate weedkiller treatments and quarantine since the weed first appeared in the 1980s. Unfortunately, desirable species typically have shorter seed lives.

Germination Rates

Those embryonic plants sink baby roots and lift their first leaves, called cotyledons, through the soil when they receive cues from their environment. These cues may be any combination of soil temperature, moisture and light and differ for each plant. By keeping seeds cool -- at 40 degrees Fahrenheit or lower -- and dry -- 8 percent relative humidity or lower -- their drive to germinate can be repressed. As seeds age, the embryos still wither, decreasing the number of viable seeds, or rate of germination. Seeds packaged for the current year should have an 80 percent or higher germination rate, but as the seed ages, the germination rate decreases.

Averages

Those pole bean seeds will have a good to excellent germination rate of 80 to 100 percent when planted the year for which they are sold. After two years, they may have a good germination rate. After three years, only 70 percent may germinate and after four years, less than 50 percent might produce plants. Each species or plant or flower ages a bit differently.

Seed Test

Germination rates are regulated by the U.S. Department of Agriculture for packaged seeds, but seeds from a seed exchange or heirloom varieties may vary. Seeds from a “Better Boy” tomato (Solanum lycopersicum “Better Boy”) might have an average four-year lifespan, but an old heirloom tomato, such as "Opaka" or "Brandywine," might have a longer or shorter average life span. To determine germination rates of old seeds, “sandwich” 10 seeds between two damp paper towels and seal them in a plastic bag for a week or more using the average germination period given on the packet. The number of seeds that germinate will indicate the approximate rates for your old seeds -- and give an indication of whether you should sow seeds more heavily or just discard them.

About the Author

An avid perennial gardener and old house owner, Laura Reynolds has had careers in teaching and juvenile justice. A retired municipal judgem Reynolds holds a degree in communications from Northern Illinois University. Her six children and stepchildren served as subjects of editorials during her tenure as a local newspaper editor.

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Reynolds, Laura. "How Does the Age of a Seed Affect Its Ability to Germinate?" Home Guides | SF Gate, http://homeguides.sfgate.com/age-seed-affect-its-ability-germinate-69423.html. Accessed 24 May 2018.

Reynolds, Laura. (n.d.). How Does the Age of a Seed Affect Its Ability to Germinate? Home Guides | SF Gate. Retrieved from http://homeguides.sfgate.com/age-seed-affect-its-ability-germinate-69423.html

Reynolds, Laura. "How Does the Age of a Seed Affect Its Ability to Germinate?" accessed May 24, 2018. http://homeguides.sfgate.com/age-seed-affect-its-ability-germinate-69423.html

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